This is not an official news source for CineForm or GoPro product releases, just some bits and pieces of stuff I happen to be working on. My work and hobbies are pretty much the same thing. -- David Newman

Wednesday, December 24, 2008

First some basics, there is no true 24p mode on standard DVD, there are is only 60i encoding (and 50i for PAL.) So all those film source are encode to DVD by adding 3:2 pulldown (or 2:2 for PAL with a 4% speed up for 24p sources.) How this pulldown is added impacts how well your DVD presents on today's common progressive displays.

Adding 3:2 pulldown for NTSC DVD creation has been has been tricky, seemingly there are lots of dead ends (like using Encore to encode directly to 24p -- this should work, I have made several blurry DVDs trying to use it.) This is one of the most common support questions. McCarthyTech has a good blog post on using AE to manually insert pulldown before encoding as 60i, and this will work everytime. It was his post that has prompted this one, as there is an even simpler way using Premiere CS3+ directly, and if you are careful it can be even better for final presentation. McCarthyTech's technique can be improved if we trust the MPEG2 encoder can to add the pulldown using repeat flags. Fortunately this works correctly using the 23.976p encode mode within Premiere's Adobe Media Encoder (MPEG2-DVD preset), now we just have to watch out for other Premiere limitations.

The advantage of pulldown that uses the MPEG2's repeat flags, this can help with quality as only fields used to construct the 24p signal are compressed, the repeat flag pad the data out to 60i. This flags also help progressive scan DVD players reconstruct the correct 24p signal more reliably. The manually created pulldown in AE works for most situations as many DVD players can use the data-rate pattern to guess the pulldown, but it is not always extracted correctly (seen as a weave pattern during motion.) Of course there is no issue for non-progressive outputs where the display is reasonable for pulldown detection (if needed.)

The way I produced several 24p DVDs in the last weeks is to export out of Premiere as a 1920×1080 24p (23.976) master CineForm AVI, then I used VirtualDub and scale using Lanzcos 3 filter to 720×480 and export out to CineForm 444 SD. Load the SD clip back into Premiere SD 24p preset, interpret footage back to 16×9, and export with Adobe Media Encoder to MPEG2-DVD 24p. Encore will take this file without further transcoding. Now that seems to be an odd path and it is, plus using VirtualDub is unnecessary, but the export to 1920x1080 master first is a very important step.

I first made the mistake of exporting my 1080p timeline directly to MPEG2-DVD, and it looks horrible. I've made this mistake before, as you simply expect it to work (never has in Premiere up to the tested PPro v3.2), but here why it doesn't always do what you want. When you add any spatial distorting filter (motion, blurs and sharpens, etc), you see the results previewed at 1080p, any scaling for your preview display is applied after the filter operations -- so you adjust you filter so they look correct on a 1080p source. We you use the Adobe Media Encoder, the scaling is applied first, before any of your filters -- as a result your output doesn't look like you previewed -- spatial filter are around 2.5 times stronger than you intended. In one of my recent projects, I was using the additional resolution of the 1080p source to reframe for a nicer DVD output, see below how much it matters in what order of operations that scale occurs (see below.)

The image on the left is soft and badly aliased, and it looks far worse in motion. Simply exporting the timeline to 1080p first, then using that new file to export to DVD solves the problem, without ever leaving Premiere. The VirtualDub step in my above technique can be as simply skipped, as loading the exported 1080p AVI into Premiere will use the CineForm importer's own Lanzcos 3 scaler for exactly the same results, much faster and more convient.

14 comments:

Hi David, how come you consider 24p with repeat flags to be 60i? Would not it be more correct to say that DVDs can be mastered in true 24p with repeat flags added if needed, a player would decode the flags and perform 2:3 pulldown in realtime and output 60i. Furthermore, many modern players can output 24p directly, so no pulldown added.

Seriously, if it is still 24p with flags, and added fields do not take extra space, it is still 24p, only flagged, is not it?

Mikus, we might be talking semantics, but think my position is more closely reflects the problems people are having when creating 24p content on SD-DVD. Clearly if there was a true 24p profile like there is in BluRay there when be no issues. The fact is there is no progressive mode on SD DVD. The MPEG2 profile encodes top fields separately to bottom fields, even if the source is progressive. The repeat flags must be added for 24p to be correctly encoded, even though it is actually encoded (sadly) as interlaced data -- (which impact compression efficiency and the ulgy 4:2:0 chroma.)

David, I see your point. Still, with extra fields being just imaginary fields because of repeat flags, I cannot accept this format as 60i. It is a field-based 24fps format, 24i perhaps? (48i in field-based notation). This does not change the way it looks, but this clears up the semantics issue for me. Thanks for heads up.

I have been working with Jake regarding writing Cineform AVI files with NeoScene for over 3 weeks. I have put a great deal of time into trying to write a 24p AVI file just as you describe here so I can create a 24p DVD.

I even hand delivered a DVD to Jake with files I created with Premiere.

You claim that this can be done from the Premiere timeline. Yet on dvinfo.net, you state that Adobe has a long standing bug in VFW and it is not possible to write a file greater than 2 gigs.

How is it possible to create a DVD as you describe here with this limitation?

Is there some technical reason why I can not do what you describe in this article?

Do you artificially impose this restriction on NeoScene and force it to use VFW rather than Direct show? I find it hard to believe that you would do this since NeoScene couldn't perform the function it was designed for without the ability.

Is there something that I am not understanding about NeoScene or about creating 24p Cineform AVI files from the Premiere timeline as you describe?

Do you have a workaround that you don't explain in this article?

I would appreciate any input you have regarding NeoScene and this issue.

I wrote this post before the consumer product Neo Scene was released, so it will not all apply. We bypass the Adobe 2GB limitation using NEO HD and Prospect HD, so you could upgrade. The issue is not VfW vs DirectShow, Adobe doesn't support DirecShow, the issue is who does the AVI creation, Adobe or CineForm. We have limiting Neo Scene to not have all the plugins of Neo HD and Prospect HD, for partical business reasons. Sometimes it is hard to find a suitable dividing line, particularly when one parent application (Premiere) has bugs, that we do fix with some of the higher-end components. Remember tools like Vegas use the same Neo Scene components and have no such issue. As we add more the CS4 support to Neo Scene will see if we can address the 2GB limitation -- it would help if more people complained to Adobe.

Thanks for your response. I can understand that you made a business decision not to allow customers to export AVI files if they use Premiere Pro but I think you may have cut the wrong feature. It seems like this should be a minimum capability for any Cineform product.

If I might point out, you mention compatibility with Premiere Pro specifically and make the following claims on your website (see below). I hope you reconsider, remove the 'If Def's from your code, and allow customers using Premier Pro to export Cineform Master files as your website mentions specifically as a feature of NewScene.

I hope you do add this feature (decide not to cut this feature for business reasons) to future releases. In any case, I love what NeoScene can do. You guys do good work.

We do all the web site suggests to the full ability of the NLE. It is Premiere Pro / AE that is limited to 2GB via VFW. So don't mis-characterize. Please write on Adobe blogs that 2GB is not a professional limitation. That said can address it, how and when is more this issue.

Thank you very much for the update to NeoScene 1.3.0. I am now able to export CF Master AVI files larger than 2 GB. I already exported a 51 minute video and the software worked perfectly. I am also able to make 24p DVDs as you describe in this article.